Personal care products generally contain one or more active ingredients within a carrier formulation. While the active ingredient(s) determine the ultimate performance properties of the product, the carrier formulation is equally critical to the commercial success of the product. The rheology of the carrier (also referred to as the “base”) largely determines the flow properties of the product, and the flow properties largely determine the manner in which the consumer will apply or use the product.
For example, aluminum chlorohydrate and aluminum-zirconium tetrachlorohydrex-Gly are metal salts that are commonly used as active ingredients in deodorant and antiperspirant products. Consumers have shown a preference for applying deodorant from a stick form. Thus, the carrier in a stick-form deodorant must be a relatively hard substance, and waxy fatty alcohol such as stearyl alcohol has been used as the carrier in these products. As another example, the active ingredient in a lipstick is the colorant. A lipstick should not be as hard as a stick deodorant, but of course must maintain its shape when undisturbed at room temperature. A blend of wax and oil is known to provide a consistency that is well-suited as a carrier for a lipstick. As a final example, shampoo desirably has a viscosity greater than water, and when the active ingredient(s) in a shampoo does not have a sufficiently high viscosity, a somewhat viscous carrier material is desirably included in the shampoo formulation.
From the above examples, it is seen that formulators of personal care products depend upon the availability of materials having various rheological properties, in order to formulate a successful personal care product. Materials which have a gel-like character, in that they maintain their shape when undisturbed but flow upon being rubbed, are often desired for personal care products.
Transparent (i.e., clear) carriers are needed by formulators who develop a personal care product wherein colorant is an active ingredient, because a transparent carrier (as opposed to an opaque carrier) will minimally, if at all, interfere with the appearance of the colorant. However, in recent years consumers have demonstrated an increasing preference for transparent personal care products such as deodorants and shampoos. There is thus an increasing demand for transparent materials which can provide the rheological properties needed for various personal care products, and particularly which can impart gel-like character to a formulation.
Polyamide resin prepared from polymerized fatty acid and diamine is reported to function as a gellant in formulations developed for personal care products. For example, U.S. Pat. No. 3,148,125 is directed to a clear lipstick composition formed from polyamide resin compounded with a lower aliphatic alcohol and a so-called “polyamide solvent.” Likewise, U.S. Pat. No. 5,500,209 is directed to forming a gel or stick deodorant, where the composition contains polyamide gelling agent and a solvent system including monohydric or polyhydric alcohols. Thus, the prior art recognizes to blend certain polyamides with alcohols, to thereby form a gel.
Certain modified polyamide resins, e.g., polyamides which are only partly amidated but contain esterified carboxyl groups, have been reported to impart high gel strength and pronounced thixotropic properties to coating compositions that contain alkyd resins or drying oils. See U.S. Pat. No. 3,141,767 to Goetze et al. However, the modified polyamide resins of Goetze et al. are not disclosed as being useful gellants in personal care products, nor useful gellants when a low polarity fluid is used as the vehicle.
Low polarity fluids are desirably included in a personal care formulation because they are often transparent, relatively inexpensive, and non-toxic. Low polarity fluids are also available in a wide variety of viscosities and grades. However, low polarity fluids often do not have the rheological properties that are desired in a carrier, e.g., they do not naturally exhibit gel-like character. There is a need in the art for materials that can be combined with low polarity solvent, such as a hydrocarbon or fatty acid ester, to afford a transparent material which has gel-like character. The gel-like character is preferably of a smooth, silky feeling when the gel is rubbed against the skin. The present invention provides this and related advantages as described herein.